what is titin

Titin, also known as connectin, is a giant protein encoded by the TTN gene in humans. It is the largest known human protein, greater than 1 µm in length, and is a family of giant elastic proteins found in vertebrate striated muscle. Titin functions as a molecular spring that is responsible for the passive elasticity of muscle. Its primary functions are to stabilize the thick filament, center it between the thin filaments, prevent overstretching of the sarcomere, and to recoil the sarcomere like a spring after it is stretched. An N-terminal Z-disc region and a C-terminal M-line region bind to the Z-line and M-line of the sarcomere, respectively, so that a single titin molecule spans half the length of a sarcomere. Titin is also known to be a regulatory node that integrates myocyte signaling pathways. The structure of titin is filamentous, and its individual domains are connected by short, flexible linkers, giving the whole structure the look of beads on a string.